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17.4
Usage Notes
The following points should be noted when using the SCI as a Smart Card interface.
Receive Data Sampling Timing and Reception Margin in Smart Card Interface Mode: In
Smart Card interface mode, the SCI operates on a basic clock with a frequency of 32, 64, 372, or
256 times the transfer rate (as determined by bits BCP1 and BCP0).
In reception, the SCI samples the falling edge of the start bit using the basic clock, and performs
internal synchronization. Receive data is latched internally at the rising edge of the 16th, 32nd,
186th, or 128th pulse of the basic clock. Figure 17-10 shows the receive data sampling timing
when using a clock of 372 times the transfer rate.
186 clocks
0
Internal
basic
clock
Receive
data (RxD)
Synchro-
nization
sampling
timing
Data
sampling
timing
Figure 17-10 Receive Data Sampling Timing in Smart Card Mode
688
372 clocks
185
371
0
Start bit
(Using Clock of 372 Times the Transfer Rate)
185
D0
371 0
D1
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